1. Field of the Invention
The present invention relates to an ignition apparatus for an internal combustion engine installed on a vehicle such as for example a motor vehicle. More specifically, the invention relates to an ignition apparatus for an internal combustion engine adapted to generate a high ignition voltage in a secondary coil of an ignition coil by interrupting a current flowing through a primary coil of the ignition coil by means of a switching element.
2. Description of the Related Art
In a known ignition apparatus for an internal combustion engine, a secondary current flowing through a secondary coil of an ignition coil is converted into a corresponding voltage by the use of a detection resistance connected with a low-voltage side of the secondary coil, so that the voltage thus converted is output as a fail signal. In addition, a common signal line is used for an ignition signal line and a fail signal line, and a mask circuit is provided that serves to force the voltage input to a switching element to discharge during the time when a fail signal is being output with an ignition signal being in an off state, so that the switching element for interrupting the supply of current to the ignition coil is prevented from being turned on by the fail signal (for example, see a first patent document: Japanese patent application laid-open No. H8-128381).
In such an ignition apparatus, however, when the switching element is turned on by the ignition signal to supply current to the ignition coil, the mask circuit might be operated by external noise so that the ignition coil could be interrupted at improper timing different from the original proper ignition timing, thus giving rise to mis-ignition or incorrect ignition.